my concern with modularity is:1) how to arrange the lower stage's 32 spheres and their tubes aerodynamically

Aerodamic drag will be an issue that will have to be dealt with. But as I said, the plan is to go through the thickest part of the atmosphere at slower speeds; less than supersonic. Your argument against that is that it will take more fuel. Yes, it will. But in the grand scheme of high costs associated with going to space, propellant costs are NOT the problem.

Dan Frederiksen wrote:

2) the double weight of a string of spheres instead of equivalent cylinder

Not if you're doing blowdown pressurization, as we plan. Spheres are best for blowdown. So I'm assuming you're suggesting we use turbopumps or some other pumps for pressurization? Uh, oh... CHACHING! There go the costs... not to mention time for development and compexity.

Dan Frederiksen wrote:

3) ensuring uniform reliable control and operation of 16 engines.

Russian Soyuz boosters regularly take off with 24 chambers firing (16 main and 8 vernier). And guess who's going to orbit the most frequently these days? In fact the Soyuz is the most reliable launch vehicle in the history of spacecraft.

Dan Frederiksen wrote:

4) the time and cost to manufacture many small instead of 1 large.

Being able to use off-the-shelf components and taking advantage of automation for as many components as possible should, on the contrary, prove less expensive and time consuming.

Dan Frederiksen wrote:

5) fueling complexity of 42 tanks.

This will prove to be a challenge, but we hope it can be overcome, and have some initial ideas on how to address it.

But Armaillo's history proves that we have humility. We aren't saying a multiple Mod cluster WILL take us to orbit, but that we think it can. The details of how many Mods are used, whether or not the upper stage will be self-pressurized LOX/LCH4, whether all or part of it will have a shroud -- all that needs to be worked out as we progress through the testing regime.

As for the rest of your arguments about Armadillo taking too long and wasting its money for what we have to show by now, we've gone through all that before. It's clear I won't be changing your mind.

As to those others who wonder why I waste my time answering Dan, even though it is clear his mind is made up and there is no convincing him, well, I find it a sort of amusing intellectual diversion. And I'm hoping others will gain understanding from it.

By the way, Dan, Wernher von Braun himself was enthusiastic about a modular approach being a viable way to reduce costs in getting to space -- he was a consultant on the OTRAG project before it was shut down for political reasons. If he were alive today, would Dan Frederiksen be presuming to lecture him on being wrong and obtuse? I bet there are a number of people in these forums that would have paid to see that.

my concern with modularity is: 1) how to arrange the lower stage's 32 spheres and their tubes aerodynamically

Nohow

Quote:

2) the double weight of a string of spheres instead of equivalent cylinder

It's not double. Even your math is wrong. Tanks themselves are about ~50% heavier when substituting spheres with same diameter but long cylinder. But then such long rocket would not be stable for powered vertical landing (see Armadillos 2005 vehicle) without large (and heavy legs).

Quote:

3) ensuring uniform reliable control and operation of 16 engines.

It has already been done 38 years ago.

Quote:

4) the time and cost to manufacture many small instead of 1 large

The whole point is that it is cheaper and simpler that way. These things do not scale linarily. 4x linearily upscaled AA's engine (which would be needed to get 16x thrust) would most proabbly melt and explode. And such heavy engine would be about 64 times heavier that current one.

Quote:

4 million dollars and 8 years

It's 1 to2 orders of magnitude lesser cost that anyone in this industry.

I take exception to the bashing of NASA by Dan. We need to remember that they are driven by mandates and operate in a very limited role in deciding what they want or can do. It would be great if their mission was to open up space for all of mankind and provide transportation to Mars and the Moon for all of us, but that has never been their mission.

They operate in a highly political environment and are subjected to the many whims of an ever changing landscape with new politicians. Yes it is frustrating what they spend and are not able to deliver what we would like. I think most of the people working there would agree with that, but they cannot operate like a private company and work towards many of the objectives that we would like. It took a new mandate by Bush to get them moving in a new direction, back to the moon. This is the reality they live in. If the new administration wants a new direction then they will again have to change course. No private company could ever function like that, or would want to.

So, it's time Sigurd. Come out of the closet and own up to it. You created "Dan" to get the conversations flowing in this forum. Didn't you?

I sit here in awe of your clever manipulation and its obvious stimulating result.

haha, I wish I was that clever... err I mean not as Dan, but to come up with such a clever solution to get things that active. After an IP check (everytime you post IP's are stored, every moderator has access to it), it shows no other username is associated with Dan, he has used two different IP's and both DNS end with .dk (denmark).

I have a redaction which I began before sebaska wrote. In my earlier quick examination I had assumed same wall thickness for cylinders of same radius as the spheres which is true for longitudinal forces but not transversal where it needs to be twice as strong, thus twice as heavy. after going over the surprisingly tricky math of comparing spheres and cylinders it seems that my intuition that a cylinder is more weight efficient than several spheres was wrong. quite to my surprise equivalent volume spheres weigh 25% less than a cylinder. it doesn't even matter how many or what proportions the cylinder has which also surprised me. maybe someone can verify the conclusion?

I still think you'd be better off with a few tanks rather than 42 but whatever the design specifics, the hope remains you make your efforts count and sooner rather than later.

OK, because he's obviously just a troll, I've stopped myself from answering any of Dan's posts... He's been an annoying diversion - even if he's gotten some interesting tidbits of information from the AA guys (c'mon people, if you wanted that info you could have asked "why do you guys do ___?" nicely).

But if he's going to start in on von Braun and Nazi-ism, its time for him to be banned. That's not what this forum is for.

But if he's going to start in on von Braun and Nazi-ism, its time for him to be banned. That's not what this forum is for.

[/lurk]

Matthew was the one who invoked von Braun in what was basically an Appeal to Authority, a bit of a rhetorical stumble there. Dan's mention of Nazis is inflammatory but essentially he's saying "von Braun wasn't always right about everything", which is the legit response to that logical fallacy.

Dan's attitude might be abrasive but I would be lying if I said I didn't empathize with him a little. I've been following Armadillo for years now and I love reading their updates even if I only understand about 1/3 of whatever the hell they're talking about. But as impressed as I am with their progress, there is often a part of me that wants to scream, "Eight years! Why the eff aren't we on the moon yet??" It wouldn't bother me if I wasn't so passionate about AA specifically.

So yeah, I appreciate getting more answers from AA. As long as Dan is asking questions that get answers, he's part of the signal. Every post complaining about what a jerk Dan is tells me nothing and is part of the noise.

They're not on the moon because they're a small outfit that spent the first few years working only as "hobbyists" after-hours and on weekends. They've gotten a HELL of a lot further than most hobby rocket folks!

They have never tried to go to the moon (or stated that as their goal), and their stated method of operation is to build and test a lot of designs and learn in an incremental fashion. That is EXACTLY what they have done. No big investments in gigantic solutions, no "hail mary" attempts. This makes the progress less-exciting for armchair enthusiasts, but it is incredibly valuable as a learning tool for the AA staff and helps them eliminate bad parts or designs and focus in on really good solutions relatively cheaply.

I'm happy that so many people are enthusiastic about space exploration and are eager to see progress, but don't blame AA for following their own path instead of the path that YOU want them to follow. If you want to chose a direction for a company or group, then you need to go found your own organization (or buy controlling interest in one).

I believe people are constantly underestimating the amount of work it takes to build a rocket. YOU may only understand about 1/3rd of what Carmack writes - but that itself is an indicator of how advanced the subject-matter is. They aren't into wasting words at AA, so even if you only get 1/3rd of it, the other 2/3rds is still important; don't underestimate that.

One more thing: Look at SpaceX. They have been at this for almost as long as AA, and have spent HUNDREDS of times more money and have a HUNDRED times more staff to throw at the problem. And after 3 very costly launch failures, they finally made it to orbit recently "after all these years".

They can't all be stupid or deliberately using less-than-optimal techniques! If it seems they're "overlooking" some obvious or simple solution, chances are there's a very good reason they're not using it.

--Noel
P.S. Also remember that a certain piece of equipment or technique *might* actually work, but they could still avoid using it for other reasons - like reliability or reusability or safety-factors or future vehicle development...

Matthew was the one who invoked von Braun in what was basically an Appeal to Authority, a bit of a rhetorical stumble there. Dan's mention of Nazis is inflammatory but essentially he's saying "von Braun wasn't always right about everything", which is the legit response to that logical fallacy.

No, he wasn't right about everything (nor did I ever suggest that). However he is widley considered to be one of the most important rocket scientists of the 20th century. But because he was also a Nazi and made rocket weapons for them, it's a rhetorical stumble to appeal to his authority on rocket science? Logical fallacy indeed.

No, appeal to authority is a logical stumble in and of itself, precisely because even an authority can and will be wrong in some cases. So the fact that some authority figure thought something doesn't prove anything, you'll need actual arguments. Another logical fallacy is appeal to numbers. Just because everyone does something in a certain way doesn't make it the best way to do it[1]. If that were true then there would never be any innovation at all.

The only real arguments in a discussion like this are numbers. But of course, doing a calculation takes some effort and requires you to know what you are talking about.

[1] Consider, for example, the case of revolving doors. People typically enter a revolving door and walk through it all the way on the outside. Walking in as straight a line as possible is more efficient: the time taken is the same, but the distance is shorter. The human brain apparently attempts to optimise the process by maximising instantaneous speed, which in this case is suboptimal. If people used their conscious minds to navigate revolving doors, they would be able to use the information they have about how the door operates to optimise their path, but they don't, and the unconscious mind is apparently unable to look ahead (a greedy algorithm like this is optimal if you know nothing about the future). Then there's the issue of stepping out of subway cars backwards, but I'll leave that for another time .

No, appeal to authority is a logical stumble in and of itself, precisely because even an authority can and will be wrong in some cases.

Yes I understand that, but it simply doesn't apply here (sorry, I should have more directly addressed that). Had I tried to argue that the modular approach was viable BECAUSE von Braun believed it was, THEN you might have something. But I neither believe that nor stated it, nor even implied it for that matter (all the actual arguments for Armadillo's belief that the modular approach might be viable had already been hashed out).

Rather, I brought up von Braun because of how amusing it was to imagine Dan Fredriksen: "Some Guy on the Internet" lecturing Wernher von Braun: "Preeminent 20th Century Rocket Scientist" on the validity of particular approaches to achieving orbit more cheaply. In other words, it was in no way in itself part of my argument for the modular approach; we've already gone through those (I guess me starting the von Braun comment with "by the way" didn't convey that well enough).

No, in my previous post what I was trying to get at was that hand-waiving dismissal of von Braun's thoughts on Rocket science because he had been a member of and built weapons for the Nazi regime is itself a [url=http://en.wikipedia.org/wiki/Non_sequitur_(logic)]Logical Fallacy[/url].

[1] Consider, for example, the case of revolving doors. People typically enter a revolving door and walk through it all the way on the outside. Walking in as straight a line as possible is more efficient: the time taken is the same, but the distance is shorter. The human brain apparently attempts to optimise the process by maximising instantaneous speed, which in this case is suboptimal. If people used their conscious minds to navigate revolving doors, they would be able to use the information they have about how the door operates to optimise their path, but they don't, and the unconscious mind is apparently unable to look ahead (a greedy algorithm like this is optimal if you know nothing about the future).

Well firstly: doing a bit of additional walking is healthy :p
Secondly: I don't agree on your argument about maintaining/maximizing speed. I think it has more to to with people's natural instinct to stay as far away from moving objects as possible (or better said: as far as is comfortable), which you can't if you are on the inside.

And of course, as always: it depends!

If the revolving door isn't powered by a motor, but has to be pushed by the persons using it, it is actually far more easy to do so on the outside because of the greater leverage.

But I somehow get the feeling, that we are getting _slightly_ off-topic...